The present invention relates to an AC power control apparatus and, more particularly, to an AC power control apparatus for controlling a turn on time or energization time of a power supply AC current supplied to a load.
In general, a heater is embedded in a windshield glass provided to a cockpit of an airplane, and a current is supplied to the heater to heat the glass so as to prevent fogging and icing. The current is supplied from an AC power supply installed in the airplane, and its value must be adjusted in accordance with an atmospheric temperature. Conventionally, the current is phase-controlled using a thyristor.
A conventional control apparatus which performs phase control using a thyristor has the following drawbacks. More specifically, an AC waveform becomes discontinuous, and causes noise. In order to prevent generation of noise, it can be considered that a current is controlled in accordance with a turn on time in units of periods of an AC current.
However, a generator installed in the airplane does not have a very good voltage fluctuation factor. Therefore, if a current is controlled in accordance with a turn on time in units of periods of an AC current, fluctuation in generator output voltage is increased, and causes fluorescent lamps for illumination to flicker.
In order to prevent discontinuity of a current, it can be considered that a plurality of power supply circuits having different powers are selectively used. In this case, when the current supply circuits having different powers are switched, a large current is instantaneously supplied due to phase mismatching of a voltage current upon switching, and a power supply voltage fluctuation may occur.
In the conventional current control circuit using the thyristor, the thyristor requires a very strict gate signal condition for turning on, and a gate signal circuit becomes complicated, resulting in high cost.